This invention relates to an apparatus and process for reducing the size of agglomerated mineral particles. More particularly, this invention relates to a rotating grizzly and to a method of using the rotating grizzly to reduce the size of mined tar sand particles to facilitate slurry preparation.
Bitumen is presently commercially extracted from mined tar sands using the Hot Water Process. In accordance with this process, the tar sand is first mixed with hot water, sodium hydroxide and steam in a rotating horizontal tumbler, called a conditioning drum. In this operation, the components of the tar sand (i.e. bitumen, water and solids) are dispersed by a combination of heating and dilution with water. More particularly, the heated tar sand comprises grains having bitumen trapped therebetween. As water is added, the sand grains collect therein; the bitumen separates from the grains and forms discrete flecks.
The slurry formed in the conditioning drum is then diluted with additional water and introduced into a separation vessel. This vessel has a cylindrical body and a conical bottom. Here, the coarse sand grains drop to the bottom of the vessel and are removed through an outlet as a tailings stream. This stream is discarded into a pond system. The bitumen flecks, which are slightly less dense than water because of the high process temperature attach themselves to gas bubbles entrained in the slurry rise through the vessel contents and form a froth product. This product overflows the vessel wall into a launder and is collected for further processing and refining. The fine solids remain largely suspended in the water of the separation vessel.
Another method of bitumen extraction from mined tar sand is provided by the Oleophilic Sieve Process disclosed in Canadian Pat. No. 1,085,760 issued on Sept. 16, 1980, U.S. Pat. No. 4,224,138 issued on Sept. 23, 1980, and U.S. Pat. No. 4,236,995 issued on Dec. 2, 1980.
In accordance with the general concepts of the Oleophilic Sieve Process, tar sand is mixed with water and usually steam to form a slurry and remove the bitumen phase from between the sand grains by a combination of tumbling, heating, and dilution with water. The slurry product is then temporarily contained or supported by an oleophilic sieve-like member. Most of the slurry solids drop through the apertures of the sieve-like member, while most of the bitumen adheres to its surface as it comes in contact therewith. The coated section of the sieve-like member then rotates or moves away from the slurry and the bitumen is recovered therefrom.
In both the Hot Water Process and the Oleophilic Sieve Process, slurry preparation is prerequisite for effective separation of bitumen from the tar sand which requires considerable mechanical and thermal energy to break down the lumps of mined tar into a smooth slurry.
The conditioning or slurry preparation step may be thought of as an ablation process where lumps of cold tar sands are tumbling in a conditioning drum. In this drum, the lumps are tumbling in the warm slurry, causing the surface of the lumps to increase in temperature and water content which results in the tar sand sloughing off these lumps to form a smooth slurry.
This ablation or heating and sloughing off mechanism requires a long residence time in the drum when the tar sand lumps are large and a progressively shorter time as the lump size of tar sand entering the drum becomes smaller.
It would therefore, be beneficial to reduce the size of the tar sand lumps prior to introduction of the mined tar sand into the conditioning drum to facilitate slurrying and reduce energy requirements.
Mined tar sands may contain other particles which require size reduction or disposal. Lumps of clay containing little or no bitumen may be present. Lumps of tar sands held together by the stickiness of the bitumen may also require reduction in size. In addition, tramp materials such as rocks, vegetation such as tree limbs, roots and trunks may be present and require separation and disposal.
There are also other types of materials which require particle size reduction which are not related to the processing of tar sands. One such example would be the breaking up of friable particles such as soft coal.
As used in this invention, all materials requiring size reduction whether homogeneous or heterogeneous will be referred to as "agglomerated" particles.